A phone screen is an important part of the interview process where the recruiter asks the candidate basic questions about their application. The questions to ask here should be basic stuff to understand the candidate more - why they applied, salary details, interview availability etc. Based on the answers, the recruiter can then ask the candidate to come for in person interview or a telephonic round with the hiring manager.
A phone screen is typically a short telephonic round, lasting about 30 minutes, during which you’ll understand the candidate's motivation and how serious they are about the interview and the opportunity. You should try understanding whether they are a good match, and are they applying for the right reasons. You should use the answers the candidates give to decide whether their profile should be sent to the hiring manager.